Multiple axle trailers

ABSTRACT

A multiple axle trailer comprises a chassis pivotally connected to turn substantially horizontally with respect to a sub-chassis and provided with means at its forward end to enable the trailer to be hitched to a towing vehicle, the sub-chassis carrying forward and rear pairs of wheels. An adjustable length steering arm is pivotally connected to the sub-chassis and to the chassis forward of the connection to the sub-chassis. A system of linkages connects the forward wheel king pins with a mounting point which is rotationally fixed with respect to the steering arm and operates to turn the forward wheels from the steering arm so that the trailer tracks the towing vehicle. In a preferred embodiment the mounting point is moveable longitudinally to enable the forward wheels to be moved in the opposite direction during reversing of the trailer.

BACKGROUND OF THE INVENTION

The present invention relates to a multiple axle trailer andparticularly to the steerage thereof.

In order to minimize wear and tear on tyres and chassis stress it isadvantageous that the trailer wheels properly follow the wheels of thetowing vehicle, be it lorry cab or tractor. To achieve this it isusually necessary that successive pairs of wheels take up slightlydifferent positions and angles under the chassis.

Existing steering systems for trailers use the bogie system for steeringby means of which both wheels of a pair are turned simultaneously byaltering the angle of the axle which connects the wheels together orallowing the rear axle wheels to pivot.

SUMMARY OF THE INVENTION

According to the present invention there is provided a multiple axletrailer comprising

a sub-chassis fitted with at least first and second axles, a chassissupported on the sub-chassis to pivot relative to the sub-chassis andprovided with means at its forward end to enable the trailer to bepivoted to a towing vehicle, a pair of wheels on the first axle able toturn with respect to the first axle,

characterized in that there is provided

a steering arm pivotally connected to the sub-chassis at a first pivot,and to the chassis at a second pivot, and adapted to pivot relative tothe sub-chassis when the chassis is caused to pivot relative to thesub-chassis, the length of the steering arm being adjustable to cater tochanges in the distance between the first and second pivots duringoperation;

a mounting point movable with the steering arm,

a respective pivot point associated with each of the first wheels,

and a system of linkages connected between each of the wheel pivotpoints and the mounting point, the linkages being operable to steer thewheels of the first axle in response to the pivotal position of thesteering arm relative to the sub-chassis.

The actual path taken by the trailer will depend on the geometry of thesteering arms.

Thus rather than taking the line of least resistance, as was the case inthe prior art, the steered wheels are actively brought to the optimumposition for following the towing vehicle.

Advantageously the sub-chassis comprises the lower part of a turntableand the chassis includes the upper part of the turn table, the pivotpoint connecting the two parts of the turntable being locatedsubstantially centrally over the axles.

The linkages may include a track arm and a track rod for each wheel ofthe first pair, each track rod having a first end pivotally mounted tothe said mounting point and a second end pivotally mounted to itsrespective track arm.

Preferably the lower part of the turntable is in the form of a square orrhombus with two opposed corners directed longitudinally of the trailer.

In one embodiment the mounting point is moveable longitudinally of thesteering arm between a position in front of an imaginary line joiningthe track rod second ends and a position behind the said imaginary line.

The adjustment of the position of the track rod mounting points in thisway alters the direction that the wheels will turn in response to anangular movement of the steering arm. For forward motion the frontwheels will be turned to track the towing vehicle while for the sameangular movement when the vehicle is in reverse the wheels will beturned the opposite way to steer the towing vehicle making reversing aseasy as a fixed axle.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example with reference tothe accompanying drawings in which:

FIG. 1 is a diagrammatic side view partially in section of a traileraccording to the invention with the chassis lifted off the sub-chassisto show the connection,

FIG. 2 is a diagrammatic plan view of the sub-chassis of the trailer ofFIG. 1,

FIG. 3 is a diagrammatic longitudinal section of the sub-chassis of FIG.1,

FIG. 4 is a diagrammatic front view of the sub-chassis of FIG. 1 showingthe arrangement of linkages,

FIG. 5 is a diagrammatic side view of a second embodiment of theinvention,

FIG. 6 is an enlarged view of part of FIG. 5

FIG. 7 is a cross section through A--A of the forward/reverse steeringmechanism of FIG. 6, and

FIG. 8 is a diagrammatic view similar to FIG. 4, but showing a rear viewof the sub-chassis.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

The illustrated trailer comprises a chassis 11 and a sub-chassis 12pivotally mounted one to the other to turn about a substantiallyvertical axis by a turntable the upper section 13 of which is housedbetween the outer beams of the chassis 11 and the lower section of whichis in the form of a frame 14 and forms part of the sub-chassis. Thepivotal mounting itself can be of any appropriate type to be smoothoperating and strong. The trailer chassis has at its front end a drawinglink 15 by means of which it can be attached to a towing vehicle.

The sub-chassis 12 which bears the weight of the trailer carries twopairs of wheels, a forward pair 16 joined together by an axle 17 andconnected via respective king pins 18 acting as pivot points to turnwith respect to the sub-chassis 12; and a rear pair of wheels 19 joinedtogether by an axle 21. The wheels 16,19 on each side of the sub-chassisare connected to one another by respective left/right walking axles22,23. The axles 22,23 which are shaped to avoid interference with theturning wheels 16, connect the axles 17,21 to a respective support beam24,25 via respective pivotal mountings 26. The support beams 24,25 eachcarry brackets 27 outward of the mounting 26 by means of which bracketsa pivotal mounting 28 is made with the sides of the frame 14 viarespective main supporting struts 29 and two balancing arms 31. All theweight of the trailer is carried at these mounting points 28. The frame14, which is supported just above the wheels, is shaped as a square orrhombus so as to avoid contact with the wheels. A circular or polygonalframe may in some circumstances be more appropriate, particularly fortrailers with more than two axles. Two opposed corners central of thesub-chassis with the diagonal beam 32 connecting them run longitudinallyof the trailer and the other two corners, connected together by thetransverse beam 33, have the struts 29 and the arms 31 attached thereto.The shape of the frame 14 is designed to allow space for the wheels andany other shape which achieves this would be satisfactory.

The front wheels 16 are turned with respect to the sub-chassis as thetowing vehicle turns by means of a steering arm 34 and a system oflinkages. The steering arm is connected at one end to the drawing link15 through a universal joint 35 connected to a bracket 36 on the link15. At its other end the steering arm 34 is connected via a universaljoint 37 to a drop arm 38 fixed to the underside of the beam 32 of theframe 14 at a position substantially mid-way between the front cornerand the centre of the frame 14.

On turning a corner, the upper part of the turn table and the towinglink automatically turn with the change of direction of the towingvehicle. Because of the resistance of the wheels on the ground this willcause the upper section of the turntable to pivot on the lower section.As a result of this relative pivotal movement between the upper andlower sections of the turntable, the distance between the pivot pointsat the extreme ends of the steering arm changes. To take account ofthis, either the steering arm may be formed telescopically or side byside in two or more parts so that it can extend and contract asrequired; or one of the ends of the steering arm may include aslide-and-pin pivot to take up the extra movement.

The former arrangement is currently preferred as it is then possible toconnect the steering arm to the towing link using a universal joint,which improves the steering. The illustrated trailer shows a telescopicarrangement with the slideably co-operating parts 41, 42.

In the embodiment illustrated in FIGS. 1 to 4 the forward wheels onlyare steerable directly from the towing link. The rear wheels are fixedangularly with respect to the sub-chassis. However as the lower part ofthe turntable pivots with respect to the upper part, the rear wheelswill turn to take up a position opposed in direction to that taken up bythe forward wheels so that a very reasonable turning circle is achieved.The forward wheels 16 are rotated on their respective king pins 18automatically by means of a linkage system taken from the steering arm34 from a position at the front of the sub-chassis 14. Each forwardwheel 16 is connected to a respective track arm 43, the track arms 43being pivotally interconnected by a track rod 44. The angular movementof the steering arm 34 is transferred into a turning of the forwardwheels 16 by a drag link 45 pivotally connected between the left wheeltrack arm 43 and to a knuckle joint 46 on the steering arm positionedunder the front end of the frame 14. It is this joint 46 that forms themounting point of claim 1.

With a distance between the two universal joints 35,37 when the traileris square on the sub chassis equal to approximately one third of thelength of the trailer, a 36 degree turn of the chassis results in a 24degree turn of the wheels 16. By adjusting the position of the bracket36 and/or the fixing point of the drop arm 38 on the frame 14, therelative turning angles of the chassis and wheels 16 can be varied.

The rear wheels can also be steered if required to take up anorientation either the same as or opposed to that of the forward wheels.This is shown in FIG. 8 which is a diagrammatic view similar to FIG. 4but showing a rear view of the sub-chassis; in it, parts which compareto those of the front wheels are shown with prime numbers. This may beachieved by a system of linkages identical to those used on the forwardwheels from a steering arm pivotally mounted between a drop arm 43'under the rear half of the frame 14 and the back end of the chassis 11.The connection between a rear drag link 45' and the steering arm willneed to be adjustable and for example a sliding joint may be used.

The connections between the walking axles 22,23 and the axles 17,21 maybe via rubber bushes. The bearings on the stearing arm need to be wellfitting to maximize the accuracy of the steering. The mounting betweenthe two sections of the turntable may include nylon (RTM) or other lowfriction bearings.

The operation of the steering system is similar to that used onautomobiles. The turning of the trailer chassis causes the upperturntable section to turn on the lower section. For a left turn thiswill result in a contraction of the steering arm and an angular movementof the steering arm. The movement of the steering arm will push the draglink 45, which in turn will push the left track arm 43 to adjust theangle of the wheel. The angular movement of the left track arm istransferred to the right track arm by means of the track rod 44.

Thus with a very simple system of linkages the forward (or rear) wheelscan be steered automatically from the alteration in direction of thefront end of the trailer.

To provide suspension the sub-chassis sections may be pivoted about atransverse horizontal axis as described above, or alternatively sprung.It may be sprung either using coil springs, or one or more leaf springs,or a single spring mounted transversely along each axle. A tie bar isrequired with a spring suspension.

The steering system is equally appropriate for agricultural and roadhaulage trailers and for twin or triple axle trailers. A twin axletrailer is described above.

FIGS. 5 to 7 illustrate a modification of the above design which is animprovement in that it operates equally well when the vehicle is beingreversed. The mechanisms are the same with regard to the connection ofthe steering arm at the front of the trailer and to the front wheel kingpins, stub axles, track arms etc, the modification being accommodatedbetween the steering arm and track arms as to be defined hereinafter.

The universal joint 37 of the mechanism of FIG. 1 is replaced by ahorizontal axis hinge 51 and a vertical axis hinge 52. The horizontalaxis hinge 51 is formed by a central portion 51a to which the steeringarm 42 is pivoted at each side. The central portion 51a is integral witha pin 52a which pin is freely pivoted within a casing 52b to form thehinge 52. The casing 52b is integral with a bracket 53 having twoapertures 54 by means of which the bracket can be mounted to the droparm 38.

The bottom end of the pin 52a is welded or otherwise fixedly connectedto a channel section member 55 the angle of which is alteredsimultaneously with the steering arm 42 parallel thereto. The channelsection member 55, which opens downwardly, carries slideably mountedtherein a track rod carrier 57 having an arm 58 which extends downwardlythrough the channel opening towards the rear end of the carrier. At thelower end of the arm 58 there is a horizontal portion 58a which isprovided with two mounting apertures 59 to which respective track rodparts 75 are fitted and which forms the mounting point of claim 1. Thesliding movement of the carrier 57 in the channel member 55 is operatedby a hydraulic or pneumatic ram 60 which is mounted above the channelmember 55 between a bracket 61 fixed to the channel member 57 and avertical extension 62 of the carrier 57. The track rod parts are eachpivotally mounted at one end to the apertures 59, and at the other endto respective track arms 64 at a respective pivot 65. An imaginary lineconnecting the pivots 65 is hereafter referred to as the "centre line".

The carrier 57 is slidable horizontally in the channel member 55 tocarry the arm 58 between a first position 66 in which the apertures 59are disposed at a predetermined distance d behind the "centre line" anda second position 67 in which the apertures 59 are disposed the samedistance d in front of the "centre line". The sliding movement betweenthe first and second positions is operated by the activation of the ram60.

For forward travel of the trailer with the arm in the first position 66the steering linkages including the divided track rod move the forwardtrailer wheels to take up a position which allows the trailer wheels totrack the towing vehicle. For reversing the trailer the track rodcarrier arm 58 is moved to its second position 67 by operating the ram60. With the arm 58 in this second position 67 the effect of rotation ofthe steering arm on the movement of the wheels is reversed so that thewheels are moved to take up a position opposed to that taken up with thearm in the first position 66. Thus the trailer is more easily reversed.The adjustment of the arm 58 will preferably be made automatically byengagement of the reverse gear in the towing vehicle. This way it is notpossible to be in the wrong position of the arm for forward or reversemovement of the trailer. Thus for forward movement of the trailer theforward trailer wheels turn in the opposite direction to those of thetowing vehicle, while for reverse movement of the trailer the forwardtrailer wheels are turned in the same direction as those of the towingvehicle.

It is preferable for the "centre line" to be vertically underneath theaxis of the hinge 52 so that the axis and the "centre line" are in thesame vertical plane. This ensures that the angle that the wheel turns inthe forward and reverse positions is the same, but opposed, for the sameangular movement of the steering arm. This is also the best arrangementto minimize the tire wear. Positioning the bracket 38 and hinge 52behind the "centre line" will result in a reduced arc of steering inforward travel with an increase in steering in reverse. The oppositeeffect can be achieved by positioning the attachment of the bracket 38and hinge 52 forwards of the "centre line".

It will be appreciated that it is possible to provide a lock on thecarrier arm 58 to fix it in at least the position 67 (and optionallyadditionally the position 66) so that, in the event of a gas (air) oroil leak, the position of the arm 58 is not altered.

Where it is required to incorporate a driven axle it may be necessary toprovide respective rams 60 for each of the two forward wheels.

I claim:
 1. A multiple axle trailer comprisinga sub-chassis fitted withat least first and second axles, a chassis supported on the sub-chassisto pivot relative to the sub-chassis and provided with means at itsforward end to enable the trailer to be pivotally mounted to a towingvehicle, a pair of wheels on each of said at least first and secondaxles, the pair of wheels on the first axle able to turn with respect tothe first axle about respective pivot points, said trailer including asteering arm pivotally connected to the sub-chassis at a first pivot,and to the chassis at a second pivot, and connected to pivot relative tothe sub-chassis when the chassis is caused to pivot relative to thesub-chassis, the length of the steering arm being adjustable tocompensate for changes in the distance between the first and secondpivots during operation; a mounting point movable with the steering arm,a respective pivot point associated with each of the wheels of saidfirst axle, and a system of linkages connected between the pivot pointof each wheel of said first axle and the mounting point, the linkagesbeing connected to steer the wheels of the first axle in response to thepivotal position of the steering arm relative to the sub-chassis.
 2. Amultiple axle trailer according to claim 1 in which the sub-chassiscomprises the lower part of a turntable and the chassis includes theupper part of the turntable, the pivot point connecting the two parts ofthe turntable being located substantially centrally over said at leastfirst and second axles.
 3. A multiple axle trailer according to claim 1in which the said mounting point is adjustable relative to the steeringarm both to a first position in which the linkages move the wheels ofthe first axle in one direction as a result of the pivotal movement ofthe steering arm and to a second position in which the linkages move thesaid wheels in the opposite direction as a result of the same pivotalmovement of the steering arm.
 4. A multiple axle trailer according toclaim 3 in which the mounting point is slidably mounted with respect toa support, the support being fixed to pivot with the steering arm, thesupport and the steering arm being mounted for pivotal movement withrespect to the sub-chassis about a substantially vertical axis.
 5. Amultiple axle trailer according to claim 4 in which the support is fixedto the steering arm via a pin and the steering arm is pivotally mountedto the said pin about a substantially horizontal axis.
 6. A multipleaxle trailer according to claim 3 in which the linkages include a trackarm and a track rod for each wheel of the first axle, each track rodhaving a first end pivotally mounted to the said mounting point and asecond end pivotally mounted to its respective track arm.
 7. A multipleaxle trailer according to claim 3 in which a lower part of the turntableis square or rhombus shaped with two opposed corners positionedlongitudinally of the trailer.
 8. A multiple axle trailer according toclaim 3 in which a second axle carries a pair of wheels mounted to turnwith respect to the second axle and means is provided to steer thewheels of the second axle from a steering arm pivotally connectedbetween the chassis and the sub-chassis.
 9. A multiple axle traileraccording to claim 1 in which the system of linkages include a track armand a track rod for at least one wheel of the first axle, said track rodhaving a first end pivotally mounted to the said mounting point and asecond end pivotally mounted to its respective track arm.
 10. A multipleaxle trailer according to claim 9 in which the mounting point ismoveable longitudinally of the steering arm between a position in frontof a line joining the track rod second ends and a position behind thesaid line.
 11. A multiple axle trailer according to claim 10 in whichthe mounting point is slidably mounted with respect to a support, thesupport being fixed to pivot with the steering arm, the support and thesteering arm being mounted for pivotal movement with respect to thesub-chassis about a substantially vertical axis.
 12. A multiple axletrailer according to claim 1 in which a lower part of the turntable issquare or rhombus shaped with two opposed corners positionedlongitudinally of the trailer.
 13. A multiple axle trailer according toclaim 1 in which the wheels of the second axle are mounted to turn withrespect to the second axle and means is provided to steer the wheels ofthe second axle from a steering arm pivotally connected between thechassis and the sub-chassis.
 14. A multiple axle trailer according toclaim 13 in which the second axle is steered from a steering armconnected between the sub-chassis and a pivot point on the chassis tothe rear of the sub-chassis.